#6
import math

AB = float(input())
CD = float(input())
R = ((AB/2)**2 + CD**2)/(CD*2)
Haob = 2*math.asin((AB/2)/R)
sector = (Haob/2)*(R**2)
triangle = 1/2*(R**2)*math.sin(Haob)
arch = sector - triangle
print(f"{arch:.2f}")